The 3000-sq-km Keo Seima (formerly called Seima Protected Forest) hosts the country’s greatest treasure trove of mammalian wildlife. Besides unprecedented numbers of black-shanked doucs and southern yellow-cheeked crested gibbons, an estimated 115 wild elephants – accounting for around a quarter of Cambodia's total population – roam the park, along with bears and cats. The Wildlife Conservation Society (WCS) helps to manage the forest, and there are a range of ecotourism initiatives under way, including primate spotting in Andong Kroloeng. The bird life is also impressive, and the jungle, which is lusher and denser than the dry forest in eastern Mondulkiri, has been relatively well preserved. Well-trained English-speaking guides accompany guests on wildlife-spotting trips for around US$85 to US$125 per person per day. Overnight stays are possible in the Jahoo Gibbon Camp, located on-site. There's a flat US$30-per-person conservation fee for both day and overnight visits. All visitors must wear neon yellow vests when entering the forest. The idea is that the primates will come to recognise yellow-vested people as harmless tourists they needn't flee from (as opposed to the drab-clothed loggers and poachers lurking on the park's periphery). The road to Sen Monorom passes right through the sanctuary, so keep an eye out for monkeys if driving through. Andong Kroloeng lies about 5km from the NH76 and about 30km from Sen Monorom. The rates include a 4WD transfer from the NH76 for the last 5km to the camp, as the road can get extremely messy in the wet season (after heavy rains, you may need to walk the last 2km). For the latest developments on tours in the park, contact the Hefalump Cafe in Sen Monorom. Book directly with either the Sam Veasna Center – based in Siem Reap and focused on extended stays, particularly for birders – or The Hangout in Sen Monorom, which is focused on more budget-friendly gibbon spotting.